In 1905, Albert Einstein, developed his Theory of Relativity. This groundbreaking piece of work changed how we think and perceive the world around us, overturning centuries of accepted scientific thinking.
My favorite analogy for the theory comes from the man himself:
"When you sit with a nice girl for two hours you think it’s only a minute, but when you sit on a hot stove for a minute you think it’s two hours. That’s relativity."- Albert Einstein
About the Theory Itself
To most it may seem like a complex mathematical solution to an esoteric problem. But how well does it explain the things we see in our daily lives?
First some clarification is in order. When we refer to the theory of relativity we need to be a bit clearer.
The special theory of relativity states that the laws of physics are equal in the universe to a stationary or non moving object or observer. In a vacuum the speed of light is constant independent of any observers. It introduced a new framework for all of physics and proposed new concepts of space and time.
But there was a problem, what about acceleration and gravity? Einstein spent the next 10 years trying to include acceleration into the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.
These two theories can be thought of collectively as the Theory of Relativity. It helps explains the motion of the planets, the effect of gravity on light to the existence of black holes.
As complex as the theory sounds it's actually surprisingly simple. First, there is no "absolute" frame of reference, hence relativity. Every time you measure an object's velocity, momentum, or passage time, it's always in relation to something else. Second, the speed of light is the constant to however measures it, whether in motion or not. Third, nothing can go faster than light.
Given all that, how can we see the effects of relativity in real life? Let's find out.
1. Global Positioning System
Without compensating for relativistic effects, a GPS unit that tells you it's, say, 0.8 km, to the next gas station would be 5 miles (8 km) off after only one day.
"Because an observer on the ground sees the satellites in motion relative to them, Special Relativity predicts that we should see their clocks ticking more slowly," explained researchers from Ohio State University.
[Image Source: Pixabay]
Why? Though not hurtling around at the speed of light, GPS satellites are going pretty fast (around 6,000 mph or 10,000 km/h). Factor in that they are sending signals to Earth's surface which is under a greater influence of the Earth's gravity. This causes a small but not imperceptible relativistic time dilation that adds about 4 microseconds each day. Add in the effects of gravity and the figure goes up to about 7 microseconds.
2. All that glitters is not gold
Most metals are "shiny" because most light is reflected with some absorbed and re-emitted as electrons "jump and fall" within orbitals.
Gold, however, is a very heavy atom. The inner electrons are moving so fast (close to half the speed of light) that their mass increases and length shortens under the effects of the Theory of Relativity. This gives them more momentum and shorter paths.
These electrons have as almost as much energy as those in the outer shells and thus wavelength absorbed and reflected are longer. This means that more light than "normal" is absorbed, which is in the blue end of the spectrum.
This means the light reflected from gold has less blue and violet in it giving gold its yellowish colour since this part of the spectrum is longer wavelength than blue.
This is a great article if you want to know more.
4. Going back to gold
The Theory of relativity doesn't just affect gold's enticing color. It also impacts on gold's ability, well inability, to react with other materials.
Gold only has one electron in its outer shell (according to Bohr's naive model), which should make it highly reactive (think of calcium or lithium). As gold is such a massive or heavy atom these electrons are held closer to the nucleus. This means that the electrons are less likely to be influenced by other atoms as they are more likely to be partying with their fellow gold electrons close to the nucleus.
Electromagnets work via relativity. When DC current flows through a single wire the conducting material is electrically neutral with no net positive or negative charge. Now lets put another identical wire next to the first.
Assuming the currents are moving and same strength, in the same direction, the electrons in the first wire "see" the electrons in the second wire as motionless. From the electrons' perspective, the protons in both wires appear to be moving. Due to relativistic length contraction, they appear to be more closely spaced, so there's more positive charge per length of wire than negative charge. Since like charges repel, the two wires also repel.
Reverse one of the currents in one of wires and you'll get the opposite effect and they will attract creating you electromagnet - awesome.
[Video Source: Veritasium]
Mercury, like gold, is a very heavy atom. As, with gold, the electrons are held closer to the nucleus (and thus have more velocity and mass than should otherwise be expected). This means that inter-atomic bonds are weak enough for Mercury to have a low melting point than other metals and thus exist in liquid state on Earth.
6. Your Old TV
Older TV's contain a piece of tech called a cathode ray tube. These work by firing electrons at a phosphor surface using a big magnet. Each electron equates to a lighted pixel on the screen. These electrons travel at about 30 percent of the speed of light and relativist effects have to be compensated for when designing the shapes of the magnets.
Isaac Newton proposed that there exists in absolute rest frame in the Universe. If this was true, then light shouldn't exist at all.
Andrew Moore of Pomona College explained it as:
"Not only would magnetism not exist but light would also not exist, because relativity requires that changes in an electromagnetic field move at a finite speed instead of instantaneously, if relativity did not enforce this requirement … changes in electric fields would be communicated instantaneously … instead of through electromagnetic waves, and both magnetism and light would be unnecessary."
8. Your very existence
All mass in our solar system came from a supernova before the birth of our sun. We are the children of this long dead Star and all heavier atoms are created and made within Supernovas.
Supernovas occur when relativistic effects overcome quantum ones in huge stars. The outer layers of a star collapse down onto the core. This then explodes, creating elements heavier than iron. In fact, nearly all the heavy elements we are familiar with today.
9. (and 10)* Nuclear Power and Sunlight
*(Ok we cheated a bit)
From nuclear power plants to our domestic star, E=MC2 describes the phenomenon of mass and energy being interconnected and convertible to one another. Without this we'd have no nuclear power and more importantly no sunlight.